1. Technical Field
The present invention is directed to a system and method for latching a micro-structure and a process for fabricating a micro-latching structure.
2. Background
Various micro-mechanical systems and micro-electromechanical systems (MEMs) are known in the art to perform various mechanical tasks. For example, Ken Goldman and Mehran Mehregany disclose a temperature memory sensor that utilizes a micro-latching mechanism in their article, xe2x80x9cA Novel Micromechanical Temperature Memory Sensor,xe2x80x9d presented at The International Conference on Solid-State Sensors and Actuators, Eurosensors IX, Stockholm, Sweden, (Jun. 25‥29, 1995). The memory sensor utilizes two separately micro-machined semiconductor layers. The semiconductor layers are positioned parallel to each other with one layer slightly overlapping the other. The memory sensor utilizes bimorph actuation to latch the two layers. Specifically, when the temperature of the sensor exceeds a predetermined temperature by a sufficient amount, the bimetallic effect causes deflection of one of the layers with respect to the other. The deflection causes one layer to be latched due to the overlapping portion of the other layer. Accordingly, the latched layer cannot return to its original position, when the memory sensor device returns to the predetermined temperature.
The memory sensor configuration is useful for temperature sensing applications. However, this configuration is not appreciably useful for other applications for various reasons. For example, the latching occurs in the same direction as bimetallic layer movement. Moreover, the memory sensor configuration only provides two possible states. Also, the memory sensor does not efficiently utilize area associated with the device.
As another example, U.S. Pat. No. 6,130,464 to Carr discloses a latching structure implemented within a micro-accelerometer. The micro-accelerometer includes a mass disposed on a cantilever. In response to acceleration, the mass exerts force on the cantilever causing it to deflect and to retract laterally over a positioned notch. The positioned cantilever is prevented from retracting due to the notch and is, therefore, latched into its rest position. The positioned cantilever may also be released from the latched position by application of current to create a thermal gradient. Additionally, the micro-accelerometer may be implemented in an in-plane configuration or in an out-of-plane configuration.
The cantilever and notch configuration of Carr is useful for accelerometer applications. However, this configuration is not appreciably useful for other applications for various reasons. For example, the latching occurs within the plane of movement of the cantilever. The disclosed cantilever and notch configuration imposes an essentially linear configuration on the device. Moreover, a very limited number of latched positions are possible according to the disclosed cantilever and notch configuration. Additionally, the disclosed cantilever and notch approach does not efficiently utilize area associated with the device.
Another micro-latching device is disclosed by Martin Hoffinan, Peter Kopka, and Edgar Voges in xe2x80x9cLensless Latching-Type Fiber Switches Using Silicon Micromachined Actuators,xe2x80x9d 25th Optical Fiber Communication Conference, OFC 2000, Baltimore, Maryland, USA, Technical Digest, Thursday, Mar. 9, 2000, p. 250-252. In the fiber switching device, the optical fibers are positioned within xe2x80x9cV-groovesxe2x80x9d and moved into position using a bi-stable actuator. The latching mechanism presented is attributed to the bi-stable actuator that takes advantage of thermally buckled cantilevers. Since the actuator has two low-energy states it can be actuated into one of the low-energy positions and will remain in that position. The latch disclosed does not fasten, or mechanically connect, the fibers into position. Rather, the mechanics holding the fibers in position are dependent on the stiffness of the bi-stable actuator. Further, the bi-stable latch device does not efficiently utilize area associated with the device.
Another micro-latching device utilizes electrostatic force to selectively latch the device into its latched position. In general, electrostatic latches provide two plates to create a capacitor. Additionally, the two plates are held apart by structure that possesses mechanical stiffness (e.g., the structure provides a spring force). Charge is provided to each plate by creating a potential difference. Additionally, a mass may be associated with one of the plates. When the mass is accelerated, the mass exerts a force against the plate causing it to be translated. If the plate is translated toward the other plate, the electrostatic force between the plates increases. When the electrostatic force becomes greater than the force provided by the mechanical stiffness of the separation structure, the plates remain in the latched position.
Electrostatic latching also possesses several disadvantages. First, electrostatic latching is not a xe2x80x9cpower-offxe2x80x9d latching mechanism. Specifically, when the potential difference between the capacitive plates is removed, the electrostatic force is removed and the device becomes unlatched. Additionally, the geometry of electrostatic latching devices is limited. Moreover, electrostatic latching devices do not efficiently utilize space.
The present invention is directed to a system and method of latching a micro-device. In embodiments of the present invention, the micro-mechanical latch comprises at least two layers. The two layers are disposed according to a defined topography. Specifically, one of the layers may possess, for example, a recess or void. The second layer possesses a protrusion that conforms to the recess or void. When the second layer is co-located with the first layer such that the protrusion superimposes the recess or void, the second layer becomes latched. Specifically, the second layer is prevented from being translated, because the first layer is operable to transmit mechanical force.
Embodiments of the present invention may be fabricated utilizing known semiconductor processing technology. In accordance with embodiments of the present invention, a first layer is provided or grown. A hole, recess, or other suitable feature is cut or etched into the first layer utilizing any suitable micro-machining technique. A sacrificial layer is created or deposited to cover the first layer. Additionally, the sacrificial layer possesses sufficiently minimal thickness to avoid completely filling the hole, recess, or other topological structure of the first layer. A third layer is then deposited over the sacrificial layer. Accordingly, conformal deposition causes the third layer to possess a complementary topography. The sacrificial layer is removed by, for example, utilizing an etching solution. The first and third layers are thereby released and may be translated with respect to each other. The first and third layers may be latched by positioning the layers to associate the complementary topography of the third layer with the hole, recess, or other topological structure of the first layer.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.